1. Field of the Invention
The present invention relates to a hinge device for use in a laptop type or portable type computer, and more particularly to a hinge device which has spring and can hold the display unit of a portable computer at a desired angle in the open position.
2. Description of the Related Art
A portable computer comprises a base unit shaped like a rectangular box. The base unit has a keyboard. A flat-panel type display unit is connected to the base unit by a hinge device.
The hinge device couples the display unit to the base unit, such that the display unit can be rotated between the closed position and the open-up position. The hinge device has a mechanism which applies a frictional drag to the display unit, thereby holding the display unit at any desired angle in a position between the closed position and the open-up position.
Published Unexamined Japanese Patent Application No 59-99111 (Published Examined Japanese Patent Application No. 63-23407) discloses a hinge device for use in portable computers, which applies a mechanism which generates a frictional drag to a display unit. This device comprises a shaft and a coil spring wound around the the shaft. One end of the coil spring is secured to the shaft, and the other end of the spring is fastened the display unit of a portable computer. As the user of the portable computer rotates the display unit with hand in one direction around the shaft, the diameter of the coil spring decreases gradually. The coil spring therefore clamp the shaft with an increasing force. As a result, the hinge device applies an increasing fictional drag to the display unit. Once the frictional drag amounts to a specific value, the hinge device holds the display unit steadily even if the user of the computer takes his or her hand off the display unit.
To build up a frictional drag to apply to the display unit, the coil spring must fit onto the shaft tightly as the user rotates the display unit with hand. It is therefore required that the shaft and the coil spring have a precise outside diameter and a precise inside diameter, respectively. Hence, much time must be spent to machine the shaft, and to form the coil spring. Also it requires much time to assemble the hinge device. The hinge device is inevitably expensive.